On February 11, 2016, the LIGO Scientific Collaboration and
Virgo Collaboration announced the first direct detection of gravitational waves (GWs)
generated by the coalescence of binary black holes (BHs) [1]}, [2]}.
It was a historical milestone for mankind to finally prove the prediction of Einstein's general relativity proposed about 100 years ago.
GWs are ripples in spacetime.
Now, it is almost common knowledge not only among scientists but also the general public that
spacetime is stretched and compressed upon the passage of GWs.
Many people are interested in GWs and general relativity; hence, it is time to think about how to cultivate its intuitive understanding [3]}.
For a good review on the history of GWs, see [4]}.
